This invention pertains to telephone and, more particularly, to party lines in a telephone system.
In order to save cable cost, it is quite common (especially in the United States) that telephone systems utilize party lines wherein a common subscriber line pair is shared by two subscribers. While party lines save cable costs, they create their own set of problems. More specifically, it is necessary to provide unique or selective ringing to each of the parties on the line. Furthermore, it is necessary to provide identification of the calling parties for billing purposes. In addition, there is the serious defect that the party on the line is afforded no privacy because the other party merely can listen in to the conversation by picking up his receiver.
In order to solve these problems, conventional party line arrangements rely on the serving telephone office being specifically designed and equipped to provide the service from a single line terminal. In addition, automatic identification relies on special circuit arrangements in the subscriber instrument to provide a ground return without adversely affecting the voice transmission. Although the utilization of special circuitry solves the first two problems, present day party lines are still confronted with the privacy problem.